Apple has admitted there is a bug with Exchange in the last release of the iOS. Users have reported that the 6.1 update has been draining their batteries quickly and excessively connecting to Exchange servers. Looks like the cause of the problem steams from when a user would respond to a recurring calendar event with a Microsoft Exchange account.
On the plus side, there is a quick fix while you wait for a official patch from Apple:
- Go to Settings > Mail, Contacts, Calendars.
- Select the Exchange account from your Accounts list.
- Turn the switch for Calendars to OFF.
- Wait ten seconds.
- Turn the switch for Calendars back to ON.
Hopefully this will help users experiencing the problem and Apple should have a patch soon.